This award will support collaborative research in cellular biochemistry between Dr. Lawrence Winship, Hampshire College and Dr. Kerstin Huss-Danell, Department of Plant Physiology, University of Umea, Sweden. The objective of the proposed research is to examine hydrogen evolution by actinorhizal root nodules. Nitrogen fixation (acetylene reduction) by actinorhizal root nodules is sensitive to changes in temperature, oxygen concentration and photosynthate supply. Each of these parameters alters the balance between oxygen diffusion into and consumption by nodules. A mechanism to protect nitrogenase from inactivation by excess oxygen as the environment changes must exist, so that the supply of fixed nitrogen to the plant can continue. Adaptive mechanisms include a variable nodule diffusion barrier and conforma- tional protection of nitrogenase. The investigators will use a unique HUP- alder symbiosis and a continuous-flow, open gas exchange system to follow in vivo nitrogenase activity and respiration. The environmental variables to be tested include oxygen concentration and temperature; measurements will include estimations of nodule gas diffusion properties, assays of nitrogenase in vitro, and immunoassays of the levels of the protein components of the nitrogenase systems. The project will benefit from the mutual expertise of the two investigators: Dr. Winship has extensive experience in conducting measurements of environmental effects on nitrogenase activity in intact plants, while Dr. Huss-Danell is well known for her studies on the physio- logical factors that affect reduction in root nodules. The results of this research will contribute to the understanding of the physiology of nitrogen-fixing actinorhizal plants.
